Research proposed on this project during the next year will be directed toward examining relationships among dietary amino acid pattern, blood amino acid pattern, brain amino acid pattern and food intake and food preferences. The approach will consist of examining the degree of competition among amino acids for uptake into brain slices. From the results of such studies, e.g. inhibition by branched-chain and aromatic amino acids of histidine uptake, diets will be devised that are predicted to inhibit the uptake of a particular amino acid into brain. These diets will then be fed to groups of rats to determine whether they result in food intake depression and depressed uptake into brain of the amino acid shown to be depressed in brain slice experiments. Plasma amino acid concentrations will also be determined. In experiments in which food intake depression is associated with altered brain amino acid pattern, concentrations of neurotransmitters, such as serotonin, will be determined. BIBLIOGRAPHIC REFERENCES: Harper, A.E. Protein and amino acids in the regulation of food intake. In: Hunger: Basic Mechanisms and Clinical Implications. D. Novin, W. Wyrwicka and G. Bray, eds. New York: Raven Press, pp. 103-113 (1976). Kohrs, M.B., A.E. Harper and G.R. Kerr. Effects of a low protein diet during pregnancy of the rhesus monkey. 1. Reproductive efficiency. Am. J. Clin. Nutr. 29: 136-145 (1976).